1. Field of the Invention
The present invention relates to a device, such as a copy machine, a printer, a facsimile, etc., that can print on both sides of sheets, and more particularly, the present invention relates to such a device that includes a memory for storing digitized images.
2. Discussion of the Background
A background printing control method of a printer is disclosed in a Japanese Patent No. 2522799. In such a control method, a controller monitors a sheet supplying operation from a sheet supplying unit and from a sheet resupplying unit. The controller controls the operations such that a sheet remaining in the resupplying unit is preferentially supplied therefrom based on a supervisory result that the sheet supplying is not to supply a sheet. Further, sheets from the resupplying unit are turned around so that the contents of each of successive original documents are printed on a back or second surface of each sheet which has already been printed on a first or front surface, and as a result, sheets having images printed on both surfaces thereof are then formed and then ejected.
However, in this method of printing on the first surface and the second surface of sheets alternately, the apparatus cannot continuously feed and keep a number of sheets with their first surface printed on which exceeds a number of standby position(s) in the apparatus, and the apparatus also must print to sheets in a given order decided before printing.
Further, increasing the number of standby position(s) in the apparatus makes the apparatus larger. Furthermore, when the apparatus has image data under compression in a storage media, because of differences in decompression times corresponding to the amount of image data, a number of sheets having their first surfaces successively printed on cannot exceed the number of standby position(s).
Furthermore, when an irregular decompression or transcription of an image data arises, re-transferring of the image data is attempted, and then a printing timing is delayed or the re-transferring may not be accomplished well.
When the re-transferring is not executed after a time, an extra process is usually executed such that a waiting operation for outputting the image data is canceled and the sheet to be printed on is ejected without printing. However, feeding a number of sheets continuously in the re-supplying path which exceeds a number of standby position(s) results in prolonging a waiting time of outputting the image data, and consequently a sheet may collide with a sheet that is in a standby position, and a sheet jam may occur. The background control method also does not operate in an apparatus having a finisher device or which takes an interrupting function into account.